What feature gives the fur seal its name and defining distinction?
Answer
A thick, dense layer of underfur beneath guard hairs
The fur seal's namesake feature is its coat, which includes a thick, dense layer of insulating underfur underneath the coarser guard hairs, a feature sea lions lack.

Related Questions
To which scientific subfamily do fur seals belong?Under which subfamily are sea lions classified?Which insulation method is primarily relied upon by sea lions?What is the characteristic vocalization often associated with sea lions?How are fur seal communications typically described?Which flippers do sea lions primarily use for underwater thrust, enabling them to "fly"?How do fur seals tend to use their hind flippers during swimming compared to sea lions?What shared ability often causes casual observers to confuse fur seals and sea lions?What feature gives the fur seal its name and defining distinction?What made fur seals an exceptionally valuable target for commercial hunting?Both fur seals and sea lions belong to which broader family of pinnipeds?